1. Field of the Invention
The present invention is generally related to a trim sensor and, more particularly, to a trim sensor system for a propulsion device of a marine vessel in which a Hall effect rotational position sensor provides a signal which is representative of the trim angle of the drive system.
2. Description of the Prior Art
Many different types of marine propulsion systems are known to those skilled in the art. One particular type of marine propulsion system comprises a drive unit attached to the transom of a marine vessel with a driveshaft extending through the transom, connecting an internal combustion engine in torque transmitting relation with the drive unit. This type of system is commonly referred to as a "stem drive system". The marine drive system is rotatable about a generally vertical axis for steering and about a horizontal axis for trim and tilt control. A sensor is typically provided to allow the trim angle of the drive unit to be monitored. Known trim sensors for marine propulsion devices utilize potentiometers or rheostats in which a moveable stylus moves across stationary conductors to provide a change in resistance that is responsive to movement of the marine drive unit.
U.S. Pat. No. 4,865,568, which issued to Koike on Sep. 12, 1989, described a trim angle sensor for a marine propulsion device. Several embodiments of trim angle sensors for marine outboard drives are disclosed. The device embodies a gear reduction unit so that the sensor will operate only over a linear portion of its operational range.
U.S. Pat. No. 4,631,035, which issued to Nakahama on Dec. 23, 1986, describes a hydraulic tilt device for a marine propulsion unit. A number of embodiments of hydraulic tilt and trim units for marine outboard drives is disclosed. The devices employ a reversible fluid pump that drives a double acting cylinder to effect pivotal movement of the outboard drive between a tilted up and a tilted down position. The circuitry of the connection between the fluid pump and motor is such that the displaced fluid from the fluid motor need not flow through the pump during tilt down operation so that tilt down operation can be accomplished at a greater rate of speed than tilt up operation.
U.S. Pat. No. 4,551,105, which issued to Hall on Nov. 5, 1985, describes a marine propulsion device with tilt and trim means with fluid filtering. The device includes a member adapted to be connected to a boat hull, and a propulsion assembly pivotally connected to the member for vertical swinging movement when the member is attached to the boat hull. The device also includes a plurality of hydraulic assemblies, each of the hydraulic cylinder assemblies including a hydraulic cylinder and a piston rod slidably received in the cylinder.
U.S. Pat. No. 5,694,039, which issued to Alfors on Dec. 2, 1997, describes an angular position sensor having multiple magnet circuits. The rotational position sensor, or angular position sensor, has two pole pieces. Each of the pole pieces has a first end portion and a second end portion. The two end portions are arranged in overlapping parallel association to provide a gap between them. Two magnetically sensitive components are disposed in the gap between the second end portions of the two pole pieces. The two magnetically sensitive components are used to provide redundancy in the event that one of the magnetically sensitive components experiences a failure.
U.S. Pat. No. 5,627,465, which issued to Alfors et al on May 6, 1997, describes a rotational position sensor with mechanical adjustment of offset and gain signals. The sensor is provided with a rotatable magnetic structure that comprises a primary magnet and a secondary magnet. The primary and secondary magnets are adjusted in position relative to each other in order to achieve an adjustability of the gain and offset characteristics of an output signal from a magnetically sensitive component disposed within the magnetic field of the magnetic structure. The primary and secondary magnets are rigidly maintained in position relative to each other and disposed for rotation about an axis of rotation. Each magnet has a magnetic axis extending through its first and second magnet poles. The two magnetic axes rotate within parallel planes that are each perpendicular to the axis of rotation of the magnetic structure.
U.S. Pat. No. 5,512,820, which issued to Alfors on Apr. 30, 1996, describes a rotational position sensor with a two-part rotatable member to resist jamming. A rotational position sensor is provided with a rotatable member that comprises first and second portions. The first portion is generally cylindrical and has an opening that is shaped to receive the second portion therein with a resilient spring disposed in the annular gap between the first and second portions when this assembly is accomplished. A magnet is molded into or otherwise affixed to an extension of the first portion and the second portion of the rotatable member is shaped to receive a shaft. Relative rotation is permitted between the first and second portions of the rotatable member so that the shaft will not be seized in position if the rotatable member is jammed within a stationary portion of the sensor.
Trim sensors that are presently used in association with marine propulsion devices typically include potentiometers. These types of devices vary the resistance of the sensor as a result of electrical contacts moving in relation to each other. If water intrudes into the housing of the device, potentiometers fail rather quickly. Since the trim sensors are located under water when associated with a marine propulsion system, intrusion of water as a result of leaks in the housing of the sensor create severe problems. Some potentiometers also have a mechanical stop included as an internal component which does not allow them to rotate freely. If these sensors are installed at an inappropriate angle, they can easily be broken if improperly installed. It would therefore be significantly beneficial if a trim sensor could be provided for a marine propulsion unit which is not rendered inoperable as a result of water leaking through a portion of the housing. It would be further beneficial if the rotational position sensor could operate without requiring that one internal component slide upon another internal component in direct physical contact with the other component.